TherapeutictimewindowisakeyelementofanydrugtotreatTBI.PatientswithmoderatetosevereTBIcanbe treated hoursafter injury;? those with mild TBI may delay treatment for days until their symptoms do notabate. FewdrugshavebeendevelopedwiththerapeutictimewindowslongenoughtotreatTBI,inpart,becauselittle is known about which cellular functions can be targeted by drugs dosed hours to days post-injury (PI). The combination of minocycline (MINO) plus N-acetylcysteine (NAC) retains high potency when first dosed 12h PI (MN12).PublishedandpreliminarydatasuggestthatMN12preventsneuronallossandprotectsdendritesinthe hippocampal ipsilateral to the impact site, allows learning of an active place avoidance task that requiresboth hippocampi;?andrestoreslatelong-termpotentiation(LTP)tobothhippocampi.Preliminarydatasuggeststhat a first dose of MINO plus NAC at 72H PI (MN72) is less potent than MN12 yet restores acquisition of Barnes maze,ataskthatrequiresonlyonehippocampus,andlateLTPinthehippocampuscontralateraltotheimpact site.MN72alsoincreasesproteinsynthesisinthecontralateralhippocampus.ThisproposalexaminesifMN12 and MN72targetdendrites, synapses, spines, and synaptic protein synthesisafter closedhead injury (CHI) in mice. Proposed studies will examine whether MN12 and MN72 targetprotein kinase M zeta (PKMz?), which is essentialforlateLTPandretentionofhippocampal-dependenttasks.StudieswillalsoexaminewhetherMINO plus NAC remains potent when dosed later than 72H PI. These data support 3 specific aims (SA) that test a centralhypothesisthat:DosingofMINOplusNACatclinicallyrelevanttherapeutictimewindowslimits graymatterinjuryandimprovescognitionandmemory.SA1:WheredoesafirstdoseofMINOplusNAC at12or72hafterCHIrepairdendrites,spinesandsynapses?TheworkinghypothesisofSA1isthatMN12 actsbilaterallytopreventinjuryandinducerepairwhileMN72actsonlyonthecontralateralhippocampus.SA1 will also assay neuroinflammation, oxidative stress and mitochondrial morphology after MN12 or MN72 treatment. SA2: Does MN12 and MN72 target PKMz? expression to restore synaptic plasticity and acquisition of hippocampal-dependent tasks? SA2 will examine a role for PKMz? expression by MN12 or MN72usingNTSA,anovelandspecificinhibitorofPKMz?,orinconditionalPKMz?mutantmice.SA2ispredicted toshowthatMN12orMN72targetPKMz?torestorelateLTPandlong-termmemory.SA3:DoesMINOplus NAClimitsbraininjuryandrestorefunctioninthesubacute(14DPI)orchronic(45DPI)stagesofTBI? The utility of MINO plus NAC would be greatly increased if the drugs retained potency when dosed in later phases of TBI. These studies have high potential significance since they show that a combination of FDA- approved drugs with clinically useful windows can restore cognition and memory, which are central deficits producedbyTBI.Thesestudieshavepotentiallyhighimpactsincetheabsenceofeffectivedrugsmakepeople withTBIlesslikelytoseektreatment.MN12andMN72areattractivecandidatesforclinicaltrialstotreatTBI.